Missoula International Airport (555 Hwy. 10 W., 406/728-4381, www.msoairport.com [1]) is just northwest of town. Alaska/Horizon, Frontier, Northwest, United, and SkyWest (Delta) Airlines fly into Missoula [2]. Shuttle service (406/543-9416) is available from the airport into town, and many hotels provide shuttles. Hertz, Budget, National, and Avis all have rental cars at the airport. Nearby (with service to the airport), find Thrifty, Enterprise, Dollar, and Alamo.
The Greyhound station is at 1660 W. Broadway (406/549-2339). Greyhound buses run three times daily along the interstate. Smaller bus lines operate out of the same terminal (same telephone number). Rimrock Trailways (800/255-7655) goes to Whitefish [3] and Billings [4].
Links:
[1] http://www.msoairport.com
[2] http://www.moon.com/destinations/montana/missoula-and-northwestern-montana/missoula
[3] http://www.moon.com/destinations/montana/missoula-and-northwestern-montana/north-flathead-lake/whitefish
[4] http://www.moon.com/destinations/montana/billings/billings